Resuscitation, as that term is herein used, refers generally to externally exerted efforts to assist or restore breathing of a patient whose natural breathing has either become impaired or has ceased, or to at least temporarily attempt to emulate the effects of more natural breathing in the patient, by forcing air or oxygen under appropriate pressure through the patient's natural airway system and into his lungs to inflate the latter at appropriate intervals separated by periods during which such application of air or oxygen under pressure is interrupted (an external physical pressure may be applied to the patient's chest) to permit the previously applied air to escape from the patient's lungs and the latter to deflate. A currently well known example is so-called "mouth-to-mouth resuscitation", in which the person administering the treatment blows air from his mouth into the mouth of the patient at rhythmic intervals and may alternately press on the patient's chest. In an environment where trained medical help is available, however, resuscitation has long normally been carried out with the assistance of various forms of resuscitator apparatus.
The forms of previous resuscitators of greatest interest as background for this invention, commonly called "squeeze bag" resuscitators, employed some type of manually compressible and self-restoring bag having the interior thereof fluid coupled to a face mask. In its most primitive conceptual form, such a device could be operated for resuscitation purposes simply by applying the mask to the face of a patient, manually squeezing the bag to force air from the bag through the mask and into the patient's lungs, releasing the squeezing pressure from the bag and removing the mask from the patient's face to permit escape of air from the patient's lungs at the same time the bag was restoring itself and thereby filling itself with fresh atmospheric air through the mask, perhaps retaining the bag in its restored condition until the time for the next bag squeezing operation, then repeating such cycle. Even in that crude form, it will be appreciated that the squeeze bag type of resuscitator offered a number of advantages as compared with other, more sophisticated types of machine powered, artificial breathing inducing equipment, including its adaptability to being portable because of its general simplicity and reliance for operating power upon merely the manual squeezing of the bag by the person administering the treatment, and its inherent characteristic of permitting a trained person administering treatment to directly control both the quantity of air forced into the patient's lungs and the intervals of doing so to best suit the size and condition of the patient through choice of the extent and timing of squeezing the bag.
Even relatively early squeeze bag resuscitators soon incorporated various refinements, including employment of resilient squeeze bags adapted to be conveniently held in one hand and to have the face mask carried more or less directly on the frontal extremity of the bag to increase portability and facilitate use by a single person, provision of a bag fill valve (an inward flow permitting check valve for communicating the interior of the bag with the atmosphere) to permit refilling of the bag with fresh air during its restoration phase without removing the mask from the face of the patient, and, in conjunction with the latter, provision of a patient non-rebreathing valve assembly interposed between the bag and the mask for in some manner permitting fresh air to move from the bag into the mask during the squeeze phase but venting air returned to the mask from the patient's lungs during the restoration or restored phases to atmosphere, rather than its passing into the bag from which it would be forced back into the patient's lungs or "rebreathed" during the next squeeze phase.
It should be noted in passing that the provision of a suitable non-rebreathing valve assembly is a non-trivial matter involving much more than merely a bag-to-mask flow permitting check valve and a mask-to-atmosphere flow permitting check valve, even to perform the basic function mentioned above, since such a pair of check valves alone would also vent to atmosphere air intended to be forced from the bag into the patient's lungs during the squeeze phase. This problem is significantly further complicated when attempt is made to safely and effectively also provide for accommodation to (rather than resistance to or suppression of) possible efforts of the patient to resume natural breathing, for protection of the patient against excessive pressures, etc. The result has been resort to a variety of types of of non-rebreathing valve assemblies of increasing complexity tending to reduce reliability, compound maintenance requirements, increase costs, and in general give rise to unnecessary practical problems for users, as well as of nature typically tending to involve compromised performance of one or more of the needed functions.
During the course of previous development of squeeze bag type resuscitators, it was recognized that it would be desirable in treating some patients to be able to administer oxygen, or at least oxygen enriched air, rather than just atmospheric air. Again, the problem was non-trivial and could not be solved merely by the continuous introduction of oxygen under pressure to the squeeze bag, since that would result in a pressure within the bag being more or less continuously communicated to the lungs of the patient through any patient non-rebreathing valve assembly adapted for performing its own primary functions, even during the restoration and restored phases of the bag cycle.
Accordingly, the development of practical means for introducing oxygen into the squeeze bag initially proceeded along lines of providing merely oxygen enrichment for the air drawn into the squeeze bag from the atmosphere during the restoration phase of the bag cycle, with the probably best (and still prevalent) approach to oxygen enrichment being to provide an elongate tube of relatively large diameter having one end thereof in fluid communication will the fill valve opening of the bag (typically at the extremity of the bag opposite from the non-rebreathing valve and mask) and the other end thereof exposed to the atmosphere, together with a considerably smaller tube extending into the larger tube and coupled with a pressurized oxygen source for continuously releasing oxygen into the air entering and accumulating within the larger tube from the atmosphere at a location typically adjacent the atmospheric side of the fill valve. Such devices are commonly called "oxygen accumulators" and are effective to introduce a mixture of air reasonably enriched with oxygen into the bag during the restoration phase of its cycle, without significantly increasing the pressure within the bag (since one end of the larger tube of the accumulator is in free communication with the atmosphere).
The advent of the oxygen accumulator did not, however, satisfy the need for being able to employ squeeze bag type resuscitators for administering substantially pure oxygen to patients under certain, relatively frequently occurring circumstances, such as various cardiac conditions. Since it has been recognized that oxygen under pressure can not be continuously introduced into the squeeze bag without defeating the other functions and essential characteristics of this type of resuscitator, known prior or concurrent development efforts of others are understood to have been or to be concentrated upon providing various valving arrangements for activating and interrupting the supply of pressurized oxygen into various parts of the resuscitator system. Such valving arrangements are intended to respond automatically to particular conditions or operating states of the resuscitator system, typically function in response to sensings of differential pressures, and are commonly referred to as "demand oxygen supply valves".
The only prior demand supply valve of which we are aware, however, was located at the front or mask end of the squeeze bag, adjacent to and in physically and functionally integrated association with the patient non-rebreathing valve, resulting im impairment of balance in the resuscitator itself, as well as impairment of needed visibility and clearance for the possible application of other medical instruments or procedures during use of the resuscitator. Moreover, the mentioned prior demand supply valve and all other demand supply valves known to now be in the process of development all involve constructions subject to various operational limitations or disadvantages involving their inability to respond rapidly, effectively, automatically and reliably to all of the diverse operating conditions that may be encountered in normal use of the resuscitator, their tendency to adversely affect operation of the closely adjacent or associated non-rebreathing valve or vice versa, or their complexity and resultant difficulty of correct disassembly and reassembly during servicing or the cleaning typically required after every use, etc.
In a very real sense, prior squeeze bag resuscitators employing demand type oxygen supply valves for administering substantially pure oxygen appear to have envolved in something of a "house that Jack built" fashion, in which additional structures have from time to time supply been added to what had existed before in an effort to add additional features recognized as desirable, but without wholly adequate correlation of individual components and their operations with either each other or the overall resuscitator apparatus. It is the purpose and, we believe, the achieved goal of this invention to provide an improved resuscitator apparatus of the mentioned type, in which at least all of the recognized limitations and disadvantages of prior devices of the same general type are eliminated through a novel and better organization and arrangement of the overall apparatus, as well as by specific improvements to the nature and construction of certain of the primary component assemblies employed in the apparatus.